Refrigerant compositions having a siloxane solubilizing agent

This application claims the priority benefit of U.S. Provisional Patent Application No. 61/048253, filed Apr. 28, 2008, which is incorporated herein by reference.

1. Field of Invention

This invention relates to a solubilizing agent for a refrigerant. More particularly, this invention relates to a solubilizing agent for improving the miscibility of conventional lubricants fluorinated-alkane, -alkene, and -ether refrigerants.

2. Description of The Related Art

Certain chlorofluorocarbons (CFCs) and hydrochlorofluorocarbon (HCFCs), such as dichlorofluoromethane (R-12), monochlorodifluoromethane (R-22), and azeotropic mixtures of monochlorodifluoromethane and chloropentafluoroethane (R-115) (known as R-502), have thermodynamic properties and chemical stability that make them useful as refrigerants. However, these chlorine-containing refrigerants are believed to interfere with the Earth\'s ozone layer. Therefore, the use of CFCs and HCFCs have become highly regulated and disfavored for heating and cooling applications.

Certain hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), hydrofluoroethers (HFEs), and blends thereof are of particular interest as alternatives to CFCs and HCFCs because they have properties that are similar to chlorofluorocarbons, including similar refrigeration characteristics, but are much more environmentally friendly. Many of these compounds have vapor pressure that is ±20 percent of a comparable CFC or HCFC refrigerant at the same temperature, and have similar chemical stability, low toxicity, non-flammability, efficiency in-use, and low temperature glides.

HFCs known to be exceptionally good refrigerants include difluoromethane (R-32), 1,1,1,2,2-pentafluoroethane (R-125), 1,1,1-trifluoroethane (R-143a), 1,1,1,2-tetrafluoroethane (R-134a), and 1,1-difluoroethane (R-152a). Certain blends of two or more of these HFCs can also be used to achieve particular thermodynamic properties. Common HFC blends include an azeotrope-like blend of R-143a and R-125 (known as R-507A), a non-azeotropic blend of R-125, R-143a, and R-134a (known as R-404A), a non-azeotropic blend of R-32 and R-125 (known as R-410A), and a non-azeotropic blend of R-32, R-125, and R-134a (known as R-407C). These alternative refrigerants are available commercially from various sources including Honeywell International Inc. of Morristown, N.J.

Each of these HFCs or HFC blends can serve as a replacement for one or more CFCs or HCFCs. For example, R-134a can serve as replacement of R-12 in refrigeration and air conditioning applications such as chillers; R-404A and R-507A can serve as replacements for R-502 in most refrigeration applications, including high, medium and low evaporation temperature systems; R410A can serve as replacement of R-22 in new air conditioning and refrigeration equipment: and R-407C can serve as a replacement for R-22 in various air-conditioning applications, as well as in most refrigeration systems including chillers. It has also become desirable to retrofit chlorine-containing refrigeration systems by replacing chlorine-containing refrigerants with non-chlorine-containing refrigerants that will not deplete the ozone layer.

To be a feasible refrigerant replacement, the HFC, HFO, or HFE must be compatible with conventional lubricants used in refrigeration systems. Refrigeration system designers are interested in how the lubricant behaves in the system so that they can design piping and other components to best manage lubricant return to the compressor. The behavior of a refrigerant with a lubricant entering the system can affect film characteristics on heat transfer surfaces, and thus energy efficiency performance. In the absence of solubility, oils tend to become lodged in the coils of the compression refrigeration, air-conditioning or heat pump system evaporator, as well as other parts of the system, thereby reducing the system efficiency. Thus, miscibility of the lubricant with the liquid refrigerant over a wide range of operating temperatures is an important consideration in selecting a refrigerant. Unfortunately, many HFCs are relatively insoluble and/or immiscible in the conventional lubricants, including mineral oils that are miscible with HCFCs. For example, mineral oil and alkyl benzenes, which have been used with conventional refrigerants such as R-12, R-502 and R-22, are immiscible with HFCs. This lack of lubricant compatibility has hindered the commercial use of many HFC as refrigerants.

HFC have been used as refrigerants in combination with alternative lubricants such as polyol ester (POE) or other synthetic lubricants. However, retrofitting refrigeration systems with HFC refrigerants is still problematic. More particularly, retrofitting refrigeration or air conditioning systems with HFC refrigerants typically requires draining as much of the lubricant oil as possible before introducing the new refrigerants with synthetic lubricants. This process often involves removing the compressor from the system so that the lubricant can be adequately drained. For these and other reasons, it would be highly desirable to retrofit a CFC or HCFC system with HFCs without having to remove the system\'s lubricant. If HFCs could be used with conventional lubricants, such a retrofit would become a simple “drop-in” operation. That is, the existent refrigerant would be replaced with a new refrigerant without any further change in, or disassembly of the system hardware.

Accordingly, there exists a need to improve the solubility of HFCs in conventional refrigeration lubricants.

Applicants have discovered that the miscibility of an HFC in conventional lubricants is unexpectedly and significantly increased by blending the HFC with a solubilizing agent comprising one or more siloxanes, and optionally, one or more hydrocarbons (HCs). In addition, it has been found that certain blends of HFCs, siloxanes, and HCs generally retain the thermodynamic properties of the HFC alone. Accordingly, blends of HFCs, HCs and siloxanes can be used to retrofit HCFC refrigeration systems without having to drain or replace the system\'s conventional lubricants.

In one aspect, the present invention provides a composition comprising: (a) a refrigerant selected from the group consisting of a hydrofluorocarbon, hydrofluoroolefin, hydrofluoroether, and blends thereof; (b) a solubilizing agent comprising at least one siloxane and, optionally, at least one hydrocarbon selected from the group consisting of: C₁-C₆ branched or straight chain alkane, alkene, or alkyl, and a C₃-C₆ cyclic hydrocarbon; and (c) a refrigeration system lubricant.

In another aspect of the invention, provided is a method for recharging a refrigerant system comprising: (a) removing at least a portion of a chlorine-containing refrigerant from a refrigeration system comprising said chlorine-containing refrigerant and a lubricant, while retaining a majority of said lubricant in said system; and (b) adding a replacement refrigerant composition to said refrigeration system either subsequent to, or simultaneously with, said removing step, wherein said replacement refrigerant composition comprises a refrigerant selected from the group consisting of hydrofluorocarbon, hydrofluoroolefin, hydrofluoroether, and blends thereof; and a solubilizing agent comprising at least one siloxane and, optionally, at least one hydrocarbon selected from the group consisting of: C₁-C₆ branched or straight chain alkane, alkene, or alkyl, and a C₃-C₆ cyclic hydrocarbon.

In another aspect of the invention, provided is a method for improving the solubility of a refrigerant in a lubricant comprising: contacting a refrigerant selected from the group consisting of a hydrofluorocarbon, hydrofluoroolefin, hydrofluoroether, and blends thereof, with a lubricant selected from the group consisting of mineral oil, hydrocarbon oil, alkyl benzene oil, white or paraffinic oil, polyalkylene glycols, polyalkylene glycol esters, polyol esters, polyalphaolefins, and combinations thereof, wherein said contacting is performed in the presence of a solubilizing agent comprising a siloxane, and optionally, at least one hydrocarbon selected from the group consisting of: C₁-C₆ branched or straight chain alkane, alkene, or alkyl, and a C₃-C₆ cyclic hydrocarbon.

In yet another aspect of the invention, provided is a refrigerant composition comprising a refrigerant selected from the group consisting of a C₁-C₆ hydrofluorocarbon, C₂-C₄ hydrofluoroolefin, C₅-C₆ hydrofluoroether, and blends thereof and solubilizing agent comprising at least one siloxane selected from the group consisting of hexamethyldisiloxane, octamethyltrisiloxane, hexaethyldisiloxane, and octaethyltrisiloxane.